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Friday, April 29, 2016

USA, Hawaii: Broken Lithosphere Could Explain Geothermal Resource

Research shows that a broken lithosphere underneath the island of Hawai'i could explain the island's patterns of seismic activity.

The deep seismic activity on the island of Hawai'i can be explained by the weight of the volcanoes atop the Earth below. Credit: NASA

In a new study, Fred W. Klein, U. S. Geological SurveyEarthquake Science Center, Menlo Park, California, USA, proposes that the flexed lithosphere beneath Hawaii, coupled with the fact that the lithospheric plate beneath the island appears to be broken—it curves downward with a central depression—explains the region’s heightened seismicity. The resulting plate flexure forms a donut hole shape right underneath the island. The focal hole in the center lies approximately between Mauna Loa, Earth’s largest active volcano, and Mauna Kea, a dormant volcano whose peak is at the highest point of Hawaii.

The author used data taken from seismic stations around the island to understand the stress fields and focal mechanisms, which describe the slip that causes earthquakes and the orientation of the fault on which those quakes occur. The seismic data give valuable information about the orientation of the stress field and the pressure and tension axis. By analyzing the seismic data, the author saw that the pressure axis—the point where two planes compress—radiated from the center of the hole in the lithosphere. These radial patterns, according to the author, suggest that the downward-flexing lithosphere surrounds a weak region at its center. (Journal of Geophysical Research: Solid Earth, doi:10.1002/2015JB012746, 2016)